1. Field of the Invention
The field of the invention relates generally to aircraft landing gear, and more particularly to improved aircraft landing gear steering systems.
2. Description of Related Art
Most aircraft, and particularly those that are heavier than air, are provided with some type of landing gear. Often such landing gear takes the form of one or more sets of freely rotateable wheels provided on respective wheel train units, which may each be independently retractable into a respective landing gear bay within the fuselage of the aircraft so as to reduce induced drag during flight. Usually, one or more of the wheel train units will also be steerable in order that a pilot can direct the aircraft on the ground. For example, it is fairly common with a tricycle-type undercarriage arrangement that the nose-wheel wheel train unit can be independently rotated relative to the aircraft fuselage in order to steer the aircraft.
Various steering arrangements for aircraft landing gear are known. One common type uses a hydraulically driven mechanical arrangement to steer aircraft [1-7]. However, the hydraulic pipes and actuators needed for such steering arrangements tend to be heavy and bulky, thereby taking up a relatively large amount of space in a landing gear bay. Additionally, hydraulic fluid is used and any leaks from such systems are problematic in the aircraft.
As an alternative to hydraulically driven arrangements, various electrically driven aircraft steering systems have also been developed [8-11]. However, these tend to be used mainly on various light aircraft because they generally have poor mechanical failure characteristics which can, for example, lead to a locking of the steering mechanism should the steering system fail. Such failure modes can be dangerous, and this is one reason why electrical steering systems have not generally been adopted for larger aircraft, such as, for example, those used for commercial air transport applications.
Additionally, certain conventional aircraft landing gear steering systems may also have poor mechanical vibration characteristics. For example, nose wheels of conventional systems can have a tendency to shimmy, or oscillate uncontrollably from side-to-side, when the aircraft touches down. This characteristic is undesirable, and may be reduced for hydraulically driven systems, for example, by providing a hydraulic accumulator and valves to increase hydraulic fluid pressure in the steering system during touch-down. Such a hydraulic accumulator and valves, however, not only add to the weight and complexity of certain conventional aircraft steering systems, but also increase the likelihood that hydraulic fluid leaks will occur.
Various aspects and embodiments of the present invention have therefore been developed whilst bearing the aforementioned disadvantages of conventional aircraft landing gear steering systems in mind.